Has anyone had experience with the Sigma 50-150mm f/2.8? It seems like it might be a good option to pair with the 17-55. It's not nearly as beefy or expensive as the Canon 70-200mm f/2.8. And with a 2X converter it gets you out to 300mm at f/5.6.

I have the earlier non-VC version for Nikon DX, and it's a treat... good image quality, repeatable focus, internal, non-extending, and parafocal.

Most of the complaints seem to be with its autofocus speed/accuracy, which isn't a concern I have.

I've been tempted by this one as well. Saw one for $540 listed online classifieds.

It looks like they have an IS and a non-IS version of the lens. I've seen some that don't have IS for that price. So if it's important to you, verify that it has IS.